CVE-2026-64525 (GCVE-0-2026-64525)

Vulnerability from cvelistv5 – Published: 2026-07-25 09:20 – Updated: 2026-10-30 12:27
VLAI
Title
xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit
Summary
In the Linux kernel, the following vulnerability has been resolved: xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit The struct pernet_operations docstring in include/net/net_namespace.h explicitly warns against blocking RCU primitives in .exit handlers: Exit methods using blocking RCU primitives, such as synchronize_rcu(), should be implemented via exit_batch. [...] Please, avoid synchronize_rcu() at all, where it's possible. Note that a combination of pre_exit() and exit() can be used, since a synchronize_rcu() is guaranteed between the calls. xfrm_policy_fini() violates this: it calls synchronize_rcu() before freeing the policy_bydst hash tables (so no RCU reader is mid- traversal at free time), but runs from xfrm_net_ops.exit -- once per namespace -- so a cleanup_net() of N namespaces pays N full RCU grace periods serially. Use the documented pre_exit/exit split. Move the policy flush (and the workqueue drains it depends on) into a new .pre_exit handler; xfrm_policy_fini() then runs in .exit and frees the hash tables after the synchronize_rcu_expedited() that cleanup_net() guarantees between the two phases. Providing O(1) RCU grace periods per batch instead of O(N). Observed on Linux 6.18 with a workload doing unshare(CLONE_NEWNET) at ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread both stuck in xfrm_policy_fini()'s synchronize_rcu(), >300k struct net accumulated in the cleanup queue, Percpu in /proc/meminfo climbed to 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and __put_net counts were balanced, ruling out a refcount leak.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6653 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 438b1f668ad58f46ce699bb48e4698a7839e3f9e , < bca6386dc08750fc7cdcbc7683473748ba3114b9 (git)
Affected: 3733fce2871c9bca9dd18a1a23b1432ea215a094 , < 91cc13978ab0bc6f669139f53e7e613a860d10e0 (git)
Affected: 069daad4f2ae9c5c108131995529d5f02392c446 , < d14ae8ef88c2c6590e107db61b6adce148cec7b3 (git)
Affected: 069daad4f2ae9c5c108131995529d5f02392c446 , < 3e52417318473782012b236d0325bf7d2266a597 (git)
Affected: b2faee12538b5b008eaef65a4201eb29cb5cefb3 (git)
Affected: b66920a3348c0f63ba18365248fa21fbf0b3a937 (git)
Affected: 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028 (git)
Affected: 6.12.83 , < 6.12.93 (semver)
Affected: 6.18.24 , < 6.18.35 (semver)
Affected: 6.1.191 , < 6.2 (semver)
Affected: 6.6.136 , < 6.7 (semver)
Affected: 6.19.14 , < 6.20 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 7.0
Unaffected: 0 , < 7.0 (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit\n\nThe struct pernet_operations docstring in include/net/net_namespace.h\nexplicitly warns against blocking RCU primitives in .exit handlers:\n\n    Exit methods using blocking RCU primitives, such as\n    synchronize_rcu(), should be implemented via exit_batch.\n    [...]\n    Please, avoid synchronize_rcu() at all, where it\u0027s possible.\n\n    Note that a combination of pre_exit() and exit() can\n    be used, since a synchronize_rcu() is guaranteed between\n    the calls.\n\nxfrm_policy_fini() violates this: it calls synchronize_rcu() before\nfreeing the policy_bydst hash tables (so no RCU reader is mid-\ntraversal at free time), but runs from xfrm_net_ops.exit -- once per\nnamespace -- so a cleanup_net() of N namespaces pays N full RCU\ngrace periods serially.\n\nUse the documented pre_exit/exit split. Move the policy flush (and\nthe workqueue drains it depends on) into a new .pre_exit handler;\nxfrm_policy_fini() then runs in .exit and frees the hash tables\nafter the synchronize_rcu_expedited() that cleanup_net() guarantees\nbetween the two phases. Providing O(1) RCU grace periods per batch\ninstead of O(N).\n\nObserved on Linux 6.18 with a workload doing unshare(CLONE_NEWNET)\nat ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread\nboth stuck in xfrm_policy_fini()\u0027s synchronize_rcu(), \u003e300k struct\nnet accumulated in the cleanup queue, Percpu in /proc/meminfo climbed\nto 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and\n__put_net counts were balanced, ruling out a refcount leak."
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    "dateReserved": "2026-07-19T15:36:31.794Z",
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    "state": "PUBLISHED"
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      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-64525.json",
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit\n\nThe struct pernet_operations docstring in include/net/net_namespace.h\nexplicitly warns against blocking RCU primitives in .exit handlers:\n\n    Exit methods using blocking RCU primitives, such as\n    synchronize_rcu(), should be implemented via exit_batch.\n    [...]\n    Please, avoid synchronize_rcu() at all, where it\u0027s possible.\n\n    Note that a combination of pre_exit() and exit() can\n    be used, since a synchronize_rcu() is guaranteed between\n    the calls.\n\nxfrm_policy_fini() violates this: it calls synchronize_rcu() before\nfreeing the policy_bydst hash tables (so no RCU reader is mid-\ntraversal at free time), but runs from xfrm_net_ops.exit -- once per\nnamespace -- so a cleanup_net() of N namespaces pays N full RCU\ngrace periods serially.\n\nUse the documented pre_exit/exit split. Move the policy flush (and\nthe workqueue drains it depends on) into a new .pre_exit handler;\nxfrm_policy_fini() then runs in .exit and frees the hash tables\nafter the synchronize_rcu_expedited() that cleanup_net() guarantees\nbetween the two phases. Providing O(1) RCU grace periods per batch\ninstead of O(N).\n\nObserved on Linux 6.18 with a workload doing unshare(CLONE_NEWNET)\nat ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread\nboth stuck in xfrm_policy_fini()\u0027s synchronize_rcu(), \u003e300k struct\nnet accumulated in the cleanup queue, Percpu in /proc/meminfo climbed\nto 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and\n__put_net counts were balanced, ruling out a refcount leak."
          }
        ],
        "id": "CVE-2026-64525",
        "lastModified": "2026-11-03T18:15:39.353",
        "metrics": {},
        "published": "2026-07-25T10:17:38.830",
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      "cve": "CVE-2026-64525",
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      "product_status:known_affected": "14",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64525.json",
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}



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